1. Field of the Invention
The present invention relates to a focus detection apparatus for a camera.
2. Related Background Art
In a typical conventional focus detection apparatus for a camera, an exit pupil of a photographing lens is divided into a plurality of areas, and relative position displacements in a plurality of images formed by beams passing through the respective pupil areas are measured to detect a focus state of the photographing lens.
More specifically, the exit pupil of the photographing lens is divided into halves by a focus detection optical system. The beams passing through the divided pupil areas are focused to form images on storage type photoelectric transducer element arrays (e.g., CCD sensor arrays). Sensor output signals are A/D-converted, and the digital signal obtained for the one or both of the areas are extracted. The extracted signals are processed to detect a relative position displacement between the two images.
In a focus state detection method of the type described above, the relative position displacement between the two images is not detected on the basis of the outputs from all pixels constituting the sensor array but is detected by shifting a pixel range of interest with all or some pixels. The factor for pixel range shifting is a focal length of the photographing lens, and optimal focus detection,is performed on the basis of the focal length.
The field of view for distance measurementexists in the center portion of the sensor array and the pixel range of the sensor which corresponds to the field of view for distance measurement is located at the center portion of the sensor array. It is preferable to perform focus detection on the basis of an output from the sensor pixel range corresponding to the center portion. However, a defocus detection ability in the pixel range of the center portion is small as compared with a case wherein all pixels of the sensor array are used. Accordingly, a focus detection disable state may be caused when focus detection is performed using the pixel range of the center portion. It is therefore preferable to perform focus detection by increasing the pixel range. Pixel range shifting on the basis of the focal length cannot solve the above problem.